Idegi plaszticitás és neuroprotekció lehetőségeinek kutatása triptofán metabolitokkal és származékaikkal = Neuronal plasticity and neuronal protection - research with triptophan-metabolites and conjugates

A pályázati támogatás olyan neuroprotekciós eljárások, anyagok kidolgozását szolgálta, mely ischemiás állapotok, traumák után fellépő hiperexcitáció csökkentésével mérsékli az ilyenkor fellépő másodlagos sejtpusztulást. A triptofán egyik metabolitja a kinurénsav (KYNA), mely az NMDA receptorok természetes inhibitoraként viselkedik a NMDA receptorokhoz kapcsolódva. A KYNA azonban nem megy át a vér-agy gáton, viszont előanyaga a kinurenin (KYN) igen. Kidolgoztunk egy módszert, melyben a KYN-t (300 mg/kg, i.p.) probeneciddel (PROB, 200 mg/kg, i.p.) együtt adva, oly mértékig meg tudjuk emelni a KYNA szintet az agyban, hogy az hatékonyan képes gátolni az agyi sérüléseket követő hiperexcitációt. Ezzel a módszerrel hatékony neuroprotekciót értünk el focalis és globalis agyi ischemiában, pentylentetrazollal (PTZ) kiváltott görcstevékenységben, de még migrén modellben is. Kifejlesztettünk két további kinurénsav származékot, a glukozamin-kinurénsavat (KYNA-NH-GLUC) és az SZR-72-nek nevezett szert, melyek szintén hatékony neuroprotektív anyagok, ugyanakkor átjutnak a vér-agy gáton, tehát szisztémásan is adhatók. Kísérleti körülmények között tehát hatékony neuroprotektív eljárást dolgoztunk ki, és hatékony anyagokat állítottunk elő. Továbbá, kimutattuk a KYNA-ról, hogy Janus-arcú, mert gátló hatása mellett, amit ?M-os koncentrációban fejt ki, ennél jóval alacsonyabb koncentrációban (200-250 nM) serkentő hatású. Mindez felveti a KYNA lehetséges neuromodulátor szerepét. | The aim of this project was to develop neuroprotective agents and protocols, which are able to reduce the late neuronal death following ischemic brain attack or brain trauma. The kynurenine pathway converts tryptophan into various compounds, including L-kynurenine (KYN), which in turn can be converted into the excitatory amino acid receptor (namely NMDA receptor) antagonist kynurenic acid (KYNA). The use of KYNA as a neuroprotective agent is rather restricted, however, because KYNA has only a very limited ability to cross the blood-brain barrier. In contrast, KYN crosses this barrier more readily. We have developed a protocol in which KYN (300 mg/kg, i.p.) administration together with probenedid (PROB, 200 mg/kg, i.p.), an organic acid transport blocker, led to significant neuroprotection in both focal and global brain ischemia, in traumatic brain attack, in migraine, and led to the inhibition of pentylenetetrazole (PTZ)-induced seizures. In addition, we have developed two kynurenic acid derivatives; glucosamine-kynurenic acid (KYNA-NH-GLUC) and SZR-72. Both of them cross the blood-brain barrier easily, and are neuroprotective agents. In addition to these experimental results, we have shown that KYNA is a Janus-faced agent, which in ?M concentration behaves as a neuroinhibitor, while in nM concentration, it stimulates the neuronal activity. This result suggests that KYNA might be play a role of a neuromodulator in the central nervoussystem

Neuroprotective effects of repeated transient global ischemia and of kynurenine adminsitration induced by four-vessel occlusions on hippocampal CA1 neurons.

The hippocampal CA1 subfield is a brain region that is particularly sensitive to hypoxia. Although this subfield is selectively vulnerable to ischemic injuries manifested in delayed neuronal death (DND), the mechanism leading to neuronal degeneration is not fully understood. Burda recently reported that a second pathophysiological stress, applied within a suitable time, offers an opportunity for salvaging neurons in the CA1 region against DND (Neurochem. Res., 30: 1397-1405, 2005). In our study, NeuN immunohistochemistry was applied to detect survival CA1 neurons, while Fluoro-Jade B staining was used to evaluate the number of injured neurons after interventions resulting in transient global ischemia. Four groups of animals were used: 1: intact controls; 2: sham controls (2 vertebral arteries coagulated (2VAC), but 2 carotids sham-operated); 3: 2VAC + 2 carotids occluded (2CA) for 10 min; 4: 2VAC + 2CA (10 min) + 2 days later, a repeated 2CA (5 min). In group 3 (2VAC + 2CA (10 min)), marked cell destruction was found in the CA1 subfield: only 36.4% of the CA1 neurons survived. However, in group 4 (5-min second ischemic insult), the proportion of surviving cells in the CA1 region was 59.3%. There was no significant difference in CA1 cell loss between groups 1 and 2. Our findings suggest that the second ischemic stress, 2 days after the first ischemia induced by 2VAC + 2CA can be efficient in the prevention of DND. Neuroprotective effect was also found in four-vessel occlusion models after kynurenine (i.v.) administration

Peripheral nerve injury influences the disinhibition induced by focal ischaemia in the rat motor cortex

Photothrombotic lesions were produced in the rat primary motor cortex, and the brain excitability was assessed in a paired-pulse stimulation protocol by transcranial recording, in parallel at 16 points of the frontal cortex, including the insulted and the surrounding areas. The cortical lesion reduced the inhibition in the extended frontal cortex, with a delay of a few minutes. Unilateral facial nerve transection, however, accelerated the widespread disinhibition. Although the mechanism is not clear in detail, both peripheral and central injury-induced disinhibition may have a significant impact on the recovery of the function